What is the concept that justifies U.S. territorial expansion throughout the Americas in the 19th century?

The idea that justifies U.S. territorial expansion throughout the Americas in the 19th century is known as Manifest Destiny. This concept held that it was the inherent right and destiny of the United States to expand its territory across the North American continent, from the Atlantic to the Pacific Ocean. Proponents of Manifest Destiny believed that this expansion was not only beneficial for the country but also a divine right ordained by God. The belief fueled various actions, including the annexation of Texas, the Oregon Trail migration, and the acquisition of lands through treaties and conflicts with Mexico.

In contrast, expansionism as a broader term refers to any policy aimed at extending a nation's influence or territory and could encompass various ideologies, while isolationism advocates for a non-involvement approach concerning foreign affairs. Colonialism involves establishing control over foreign territories and exploiting their resources, which does not quite capture the self-justifying nature and ideological underpinnings of Manifest Destiny. Thus, the specific justification for 19th-century U.S. territorial growth is rooted in the belief in Manifest Destiny.